Property, plant and equipment and assets held for lease (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Finance and Financial Products [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment and assets held for lease, gross	$ 13,930	$ 13,428
Property, plant and equipment and assets held for lease, accumulated depreciation	(3,993)	(3,739)
Total property, plant and equipment and assets held for lease, net	9,937	9,689
Finance and Financial Products [Member] | Assets held for lease [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment and assets held for lease, gross	$ 12,287	11,902
Finance and Financial Products [Member] | Assets held for lease [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	5 years
Finance and Financial Products [Member] | Assets held for lease [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	35 years
Finance and Financial Products [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment and assets held for lease, gross	$ 230	224
Finance and Financial Products [Member] | Buildings, machinery and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment and assets held for lease, gross	$ 1,413	1,302
Finance and Financial Products [Member] | Buildings, machinery and other [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	3 years
Finance and Financial Products [Member] | Buildings, machinery and other [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	50 years
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 36,971	35,011
Property, plant and equipment, accumulated depreciation	(17,025)	(15,686)
Total property, plant and equipment, net	19,946	19,325
Insurance and Other [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,226	2,108
Insurance and Other [Member] | Buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 8,631	8,360
Insurance and Other [Member] | Buildings and improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	5 years
Insurance and Other [Member] | Buildings and improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	40 years
Insurance and Other [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 21,409	20,463
Insurance and Other [Member] | Machinery and equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	3 years
Insurance and Other [Member] | Machinery and equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	25 years
Insurance and Other [Member] | Furniture, fixtures and other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 4,705	4,080
Insurance and Other [Member] | Furniture, fixtures and other [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	2 years
Insurance and Other [Member] | Furniture, fixtures and other [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	15 years
Railroad [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 70,260	67,380
Property, plant and equipment, accumulated depreciation	(8,293)	(6,130)
Total property, plant and equipment, net	61,967	61,250
Railroad [Member] | Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	6,085	6,063
Railroad [Member] | Track structure and other roadway [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 50,789	48,277
Railroad [Member] | Track structure and other roadway [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	9 years
Railroad [Member] | Track structure and other roadway [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	100 years
Railroad [Member] | Locomotives, freight cars and other equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 12,459	12,075
Railroad [Member] | Locomotives, freight cars and other equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	6 years
Railroad [Member] | Locomotives, freight cars and other equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	41 years
Railroad [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 927	965
Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	90,808	87,172
Property, plant and equipment, accumulated depreciation	(25,829)	(24,663)
Total property, plant and equipment, net	64,979	62,509
Utilities and Energy [Member] | Utility generation, transmission and distribution systems [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 73,138	71,536
Utilities and Energy [Member] | Utility generation, transmission and distribution systems [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	5 years
Utilities and Energy [Member] | Utility generation, transmission and distribution systems [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	80 years
Utilities and Energy [Member] | Interstate natural gas pipeline assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 6,991	6,942
Utilities and Energy [Member] | Interstate natural gas pipeline assets [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	3 years
Utilities and Energy [Member] | Interstate natural gas pipeline assets [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	80 years
Utilities and Energy [Member] | Independent power plants and other assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 7,176	6,596
Utilities and Energy [Member] | Independent power plants and other assets [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	3 years
Utilities and Energy [Member] | Independent power plants and other assets [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	30 years
Utilities and Energy [Member] | Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 3,503	2,098
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, net	$ 126,946	$ 123,759